This invention relates to ink jet printing devices and more particularly to thermal ink jet printheads having a patternable ink flow directing channel structure.
In one conventional thermal ink jet printhead, the printhead consists of two sections, a heater plate and a channel plate. Some geometrical features are formed in both plates in such a way that, when bonded together, they form the desired configuration for ink droplet ejection. For example, U.S. Pat. No. 4,774,530 discloses a printhead in which upper and lower silicon substrates are mated and bonded together with a thick film insulative layer sandwiched therebetween. One surface of the upper substrate or channel plate has a plurality of parallel grooves and a recess etched therein. When mated with the lower substrate or heater plate, the grooves and recess form the printhead ink channels and ink reservoir, respectively. The grooves are open at one end and closed at the other end. The channel open ends serve as the printhead nozzles. The channel closed ends are closely adjacent the reservoir and placed in fluid communication therewith by a patterned recess in the thick film layer. Each channel is capillarily filled with ink from the reservoir and has a heating element located upstream of the nozzles. Each heating element is selectively driven by electrical pulses representative of data signals to produce momentary vapor bubbles in the ink to effect the ejection of ink droplets from the printhead nozzles and propel them to a recording medium. The thick film layer is also patterned to expose the heating elements and thereby place the heating elements in a pit to better contain the vapor bubble and prevent ingestion of air.
This printhead construction has some drawbacks. For example, the silicon channel plate is anisotropically or orientation dependent etched to form straight, triangularly shaped grooves when non-straight grooves provides more design flexibility and non-triangular shaped nozzles assist in droplet directionality. In addition, an etched silicon channel plate means separate fabrication of the two plates and the necessity of very accurate alignment between the two when they are mated. Because silicon is opaque, it is difficult to determine if the adhesive is coating all of the surface areas required to separate the channels and to prevent internal ink leaks.
U.S. Pat. No. 5,132,707 discloses a thermal ink jet printhead having an array of coplanar nozzles in a nozzle face that are entirely surrounded by a polymeric material. The ink channels, nozzles, and ink reservoir are produced by sequentially depositing and patterning two layers of polymeric material, such as, for example, Vacrel.RTM., on the heater plate, so that the heating elements are placed in a pit in the first layer and the channels and reservoir recesses are produced in the overlying second layer. The cover plate has a third layer of identical polymeric material with a hole through both the cover plate and third layer to serve as the ink inlet. The cover plate with the third layer is aligned and bonded to the second layer with the cover plate hole aligned with the reservoir recess in the second layer to produce the printhead.
U.S. Pat. No. 5,198,834 discloses a printhead or pen head for a droplet-on- demand ink jet printer or pen which utilizes a barrier wall located between a substrate and an orifice plate. The ink flows through the printhead in channels defined in the barrier wall. The barrier wall is fabricated in two layers from cured, photoimaged resist materials. One layer is a soldermask material, and the other is a photolithographic resist material. The two layers together resist chemical attack by the ink and separation of the orifice plate from the printhead.
Pending U.S. patent application Ser. No. 08/712,761, filed Sep. 12, 1996, entitled "Method and Materials For Fabricating An Ink Jet Printhead," and assigned to the same assignee as the present invention discloses an ink jet fabrication technique which enables capillary channels for liquid ink to be formed with square or rectangular cross-sections. A sacrificial layer is placed over the main surface of a silicon chip, the sacrificial layer being patterned in the form of the void formed by the desired ink channels. A permanent layer comprising a permanent material is applied over the sacrificial layer and, after polishing the two layers to form a uniform layer which exposes some of the surfaces of the sacrificial layer, the sacrificial layer is removed to form open ink channels. A cover plate is bonded to the patterned permanent material to provide the closed ink channels and produce the printhead. Preferred sacrificial layer materials include polyimide while the preferred permanent layer materials include polyarylene ether ketone.